What Then?

Does the physical world exist, or are ideas all that there is?
This old philosophical question can never be proven one way or another, despite the best efforts of Berkeley to argue one side and Russell arguing the other. In fact, not only can it not be proven, but the question cannot even be interpreted in a way that has any meaning. What does it mean to exist? Is existence a predicate?
It can be frustrating that questions that we feel ought to have both a meaning and an answer appear to have neither. After some irritable chawing away at the discomfort this causes me, I have come up with a solution. I call it the ‘what then?’ test. This goes as follows:
For any given question with which we are faced, we should first ask: ‘if the answer is yes, what then?’ If the answer is ‘nothing of consequence’ then it probably means the question is unimportant, and quite likely also meaningless.
Some questions have obvious significant consequences, for example:

Is that a gun in your pocket?

What time shall I meet you?

Is it right for me to eat meat?

Others have significant consequences that only become apparent after some consideration, for example:

are animals conscious?

Is there a god that is a person and who is all-powerful?

Is Cartesian dualism true?

The first has important consequences because whether animals are conscious, and hence capable of suffering, is critical to our assessing the ethics of how we treat them.
The second has important consequences because, if there is an all-powerful, all-knowing being with opinions, desires and an interest in humans, we may be able to obtain advantage by pleasing it, or at least avoid punishment by not displeasing it.
The third has the important consequence that, if the answer is yes, it opens the possibility that the mind could survive without the body, and thereby that a continuation of conscious life after death may be possible.
But for some questions, one cannot find any consequences for our lives. Here are some examples:

Do propositions about the future have a truth value?

If there were no humans or other sentient beings, would moral values still exist?

Is Idealism true?

Do objects exist about which nobody can ever have any information?

Is there a world of Platonic forms?

If a tree falls in the forest and there is nobody there to hear it, does it make a sound?

I just cannot see any way that the answers to these questions have any consequences for us, one way or the other. In the light of that, it seems that these questions are useless to us, and not worthy of consideration.
But I think we can make a stronger statement than that. I think we might actually be able to say that questions that have no consequences have no meaning. How can one define a meaning for a concept that does not in some way touch upon our experience? I can’t say for sure that one cannot. But when I look at the concepts for which there are clear meanings, they all derive ultimately from simpler concepts based on past or potential future experience.
Take something very abstruse and seemingly far removed from everyday reality – the wave functions of quantum mechanics. These are elements of infinite-dimensional Hilbert spaces. What relevance could such a complex and abstract thing have to my life? The answer is that analysis of the mathematics of those wave functions allows predictions to be made about what I will experience in future, and that is part of my real life. When I press a button on my MP3 player, it plays the track I expect because of the quantum mechanics that govern the tiny electronics inside it.
Now take a question that appears to be very simple, but which has no impact on my everyday life. ‘Do things exist of which neither I nor anybody else will ever be aware?’ The naive physical answer to this is ‘of course’: there are rocks buried deep in the Earth that no creature has ever seen. There are stars in distant galaxies, from which no light has ever reached the Earth.
‘Yes’, says the sceptical philosopher, ‘but how do you know they are really there? How do you know that anything that is not currently being immediately sensed by you exists?’
The answer is that I don’t. The model of the universe in my brain says that there are rocks deep underground that I will never see, but I cannot categorically state that they exist.
Does this create a state of confused scepticism? No, because, if I was particularly concerned about what sort of rock lies five metres beneath my feet I could dig down and have a look. If I want to know whether the universe still exists outside my field of vision I can turn around. Of course it’s possible that the evil demon whose job it is to trick me quickly conjures up that part of the world just before I turn around. But then my special question comes into play: ‘what then?’ What difference does it make whether the world existed while I wasn’t looking? The only way that it makes any difference is if, at some future time, the demon will leap out in front of me and shout ‘April Fool!’ But that’s not the scenario Descartes had in mind when he imagined this demon. He imagined the demon would always be there, always maintaining the illusion of a complete physical universe. If so, then it is of no consequence to me whether the universe is real or a demonic illusion, as it will never have any impact on me or anybody else, one way or another.
Further, there is no real meaning to the question of whether the demon is there. What do I mean by a demon being there? The only meaning that can be ascribed to it is that there is a creature behind me that I or somebody else could see if we looked quickly enough. But by definition we cannot look quickly enough, so that meaning does not work. We cannot say that the demon is there and mean anything by it. Every statement we make about the existence or otherwise of objects, and the properties and relationships they may have, is based on the object, its properties or its relationships with other objects being able to be perceived through our senses, either directly, or indirectly through circumstantial evidence.
I conclude that any proposition whose truth or falsity cannot be ascertained now or at some time in the indefinite future by one or more sentient beings is meaningless. That probably accounts for at least half of metaphysics (but not all of it).
An uncomfortable apparent corollary of this conclusion is that perhaps even the question of whether we have free will is inconsequential and probably meaningless. It is hard to imagine any test that would irrefutably determine whether we have free will, so does that just make it an empty question like the others above? I think the answer is that it does as far as my own free will goes. I will never be able to be sure whether or not I have free will, so I should stop thinking about it. However it is important in relation to what I think about other people’s free will. Given the strong doubt about whether free will exists, or even means anything, I should avoid blaming others for their moral choices or seeking retribution against them, except where I think that would serve some socially beneficial purpose.